The invention relates to a centrifugal separator for the concentration of suspended solids having outlet valves disposed uniformly on the circumference preferably in the plane of the greatest separating chamber diameter. The outlet valves have movable valve pistons which are shielded from the pressure of the drum charge by a valve casing and which close nozzle orifices by centrifugal force during operation of the drum at full rotatory speed and assume an open position upon the introduction of a control liquid.
Centrifugal separators of such construction are known. It is a disadvantage of these drums that the valve provided for the removal of concentrate can assume either a closed or an open position, and fine regulation of the nozzle aperture size is not possible since the valves have conical seats which are not suitable for fine adjustment according to the concentration and particle size of the solids.
When suspended solids are to be concentrated, a high concentration of the solids is desirable, the nozzle aperture size and the number of nozzles being determined on the basis of a constant rate of flow and a constant solid particle size. Under the high liquid pressure in the drum, therefore, it is necessary, especially in the case of low rates of flow of the solids, to have very small nozzle apertures, e.g., under 1 mm in diameter, if they are disposed at the periphery of the drum, in order to achieve a sufficient concentration of the solids. Larger nozzles can be used only if the nozzles are disposed on a smaller drum diameter, and if the solid particles are of a light consistency and slide off inwardly on a smaller diameter. The nozzles, however, must be disposed at the periphery of the drum when the particles are of a higher specific weight and are unable to slide off on a smaller diameter.
In nozzles of small aperture size, however, even if the material has been well screened beforehand, it is easily possible for the nozzles to become clogged, for example by the loosening of deposits of solids. This not only impairs the operation of the centrifuge, but can result in imbalances which can lead to considerable damage. The danger is all the greater the smaller the nozzle aperture is, and therefore apertures are not made smaller than a certain minimum diameter. When the solid content of the liquid being separated is low, the result of this is that the use of nozzle-type centrifuges is possible only by the use of partially disadvantageous measures, such as the use of a smaller number of nozzles or of the recycling of the concentrate. One particular disadvantage in the case of a fixed nozzle cross section is that the amount of solid substance produced must not vary during operation, because otherwise either the concentrate becomes too thin, or nozzle clogging occurs.